Method and apparatus for detection of orifice clogging in pressure-type flow rate controllers

1. A method of detecting clogging of an orifice in a pressure-type flow rate controller which has a control valve (CV), an orifice (2), a pressure detector (14) for measuring the upstream pressure P.sub.1 therebetween, and a flow rate setting circuit (32) wherein, with the upstream pressure P.sub.1 maintained about two or more times higher than the downstream pressure P.sub.2, the downstream flow rate Q.sub.C is calculated with the equation Q.sub.C =KP.sub.1 (K=constant) and wherein the control valve (CV) is controlled on the basis of the difference signal Q.sub.Y between the calculated flow rate Q.sub.C and the set flow rate Q.sub.S, said method comprising: a first step of holding the set flow rate Q.sub.S at a high set flow rate Q.sub.SH, a second step of switching from the high set flow rate Q.sub.SH to a low set flow rate Q.sub.SL and maintaining the low set flow rate Q.sub.SL and determining the upstream pressure P.sub.1 to obtain the pressure attenuation data P(t), a third step of checking said pressure attenuation data P(t) against standard pressure attenuation data Y(t) measured under the same conditions as with the pressure attenuation data P(t) but with the orifice not clogged, and a fourth step of turning on a clogging alarm when the pressure attenuation data P(t) deviates from standard pressure attenuation data Y(t) by at least a specific degree.

2. The method of detecting clogging of an orifice in a pressure-type flow rate controller as defined in claim 1, wherein, with the high set flow rate Q.sub.SH at 100 percent of the flow rate (full scale flow rate) and the low set flow rate Q.sub.SL at 0 percent (the control valve kept completely closed), the clogging alarm will be turned on when the pressure attenuation data P(t) at the lapse of a specific time after the switching of the flow rate to the low set flow rate deviates from standard pressure attenuation data Y(t) by at least a specific degree.

3. The method of detecting clogging of an orifice as defined in claim 1 or claim 2, wherein standard pressure attenuation data Y(t) and pressure attenuation data P(t) are given in the form of Y(t)=exp (-kt) where k is an attenuation parameter.

4. A method of detecting clogging of an orifice in a pressure-type flow rate controller which has a control valve (CV), an orifice (2), a pressure detector (14) for measuring the upstream pressure P.sub.1 therebetween, and a flow rate setting circuit (32) wherein, with the upstream pressure P.sub.1 maintained about two or more times higher than the downstream pressure P.sub.2, the downstream flow rate Q.sub.C is calculated with the equation Q.sub.C =KP.sub.1 (K=constant) and wherein the control valve (CV) is controlled by the difference signal Q.sub.Y between the calculated flow rate Q.sub.C and the set flow rate Q.sub.S, the method comprising: a first step of holding the set flow rate Q.sub.S at the high set flow rate Q.sub.SH ; a second step of switching from the high set flow rate Q.sub.SH to the low set flow rate Q.sub.SL and maintaining the low set flow rate Q.sub.SL, measuring the upstream pressure P.sub.1 and the upstream temperature T.sub.1, and working out pressure attenuation data P(t) from those measured values; a third step of checking said pressure attenuation data P(t) against standard pressure attenuation data Y(t) worked out from the upstream temperature T.sub.1 and the upstream pressure P.sub.1 measured under the same conditions as with the pressure attenuation data P(t) but with the orifice not clogged; and a fourth step of turning on a clogging alarm when the pressure attenuation data P(t) deviates from standard pressure attenuation data Y(t) by at least a specific degree.

5. The method of detecting clogging of an orifice as defined in claim 4, wherein, with the high set flow rate Q.sub.SH at 100 percent of the flow rate (full scale flow rate) and the low set flow rate Q.sub.SL at 0 percent (the control valve kept completely closed), the clogging alarm will be turned on when the pressure attenuation data P(t) at the lapse of a specific time after the switching of the flow rate to the low set flow rate deviates from standard pressure attenuation data Y(t) to at least a specific degree.

6. The method of detecting clogging of an orifice as defined in claim 4 or claim 5, wherein the standard pressure attenuation data Y(t) and pressure attenuation data P(t) are worked by the formula: ##EQU4## where P.sub.o, C.sub.o, R.sub.o, and T.sub.0 are the standard time upstream gas pressure, constant of gas specific heat ratio, gas constant, and gas temperature, respectively, and P.sub.t, C.sub.t, R.sub.t, and T.sub.t are the arrival time upstream gas pressure, constant of gas specific heat ratio, gas constant, and upstream temperature, respectively.

7. An apparatus for detecting clogging of an orifice in a pressure-type flow rate controller which has a control valve (CV), an orifice (2), a pressure detector (14) for measuring the upstream pressure P.sub.1 therebetween, and a flow rate setting circuit (32) wherein, with the upstream pressure P.sub.1 maintained about two or more times higher than the downstream pressure P.sub.2, the downstream flow rate Q.sub.C is calculated with the equation Q.sub.C =KP.sub.1 (K=constant) and wherein the control valve (CV) is controlled by of the difference signal Q.sub.Y between the calculated flow rate Q.sub.C and the set flow rate Q.sub.S, said apparatus comprising: a storage memory M memorizing standard pressure attenuation data Y(t) of the upstream pressure P.sub.1 measured with the flow rate switched from the high set flow rate Q.sub.SH to the low set flow rate Q.sub.SL with the orifice (2) not clogged, a pressure detector (14) for determination of the pressure attenuation data P(t) of the upstream pressure P.sub.1 with the flow rate switched from the high set flow rate Q.sub.SH to the low set flow rate Q.sub.SL with the orifice (2) in the actual conditions, a central processing unit CPU for checking the pressure attenuation data P(t) against standard pressure attenuation data Y(t), and an alarm circuit (46) for turning on a clogging alarm when the pressure attenuation data P(t) deviates from standard pressure attenuation data Y(t) by at least a specific degree.

8. The apparatus for detecting clogging of an orifice as defined in claim 7, wherein standard pressure attenuation data Y(t) and pressure attenuation data P(t) are given in the form of Y(t) {or P(t)}=exp (-kt) where k is an attenuation parameter.

9. An apparatus for detecting clogging of an orifice in a pressure-type flow rate controller which has a control valve (CV), an orifice (2), a pressure detector (14) for measuring the upstream pressure P.sub.1 therebetween, and a flow rate setting circuit (32) wherein with the upstream pressure P.sub.1 maintained about two or more times higher than the downstream pressure P.sub.2, the downstream flow rate Q.sub.C is calculated with the equation Q.sub.C =KP.sub.1 (K=constant) and wherein the control valve (CV) is regulated by the difference signal Q.sub.Y between the calculated flow rate Q.sub.C and the set flow rate Q.sub.S, the apparatus comprising: a pressure detector (14) for measuring the pressure P.sub.1 upstream of the orifice; a temperature detector (24) for detecting the upstream temperature T.sub.1 ; a storage memory M memorizing standard pressure attenuation data Y(t) of the upstream pressure P.sub.1 worked out from the upstream temperature T.sub.1 and the upstream pressure P.sub.1 measured with the flow rate switched from the high set flow rate Q.sub.SH to the low set flow rate Q.sub.SL with the orifice (2) not clogged; a central processing unit CPU for working out the standard pressure attenuation data Y(t), calculating the pressure attenuation data P(t) for the upstream pressure P.sub.1 on the basis of the upstream pressure P.sub.t and upstream temperature T.sub.t measured with the flow rate switched from the high set flow rate Q.sub.SH to the low set flow rate Q.sub.SL with the orifice (2) in the actual conditions, and checking the pressure attenuation data P(t) against the standard pressure attenuation data Y(t); and an alarm circuit (46) for turning on a clogging alarm when the pressure attenuation data P(t) deviates from standard pressure attenuation data Y(t) to at least a specific degree.

10. The apparatus for detecting clogging of an orifice as defined in claim 9, wherein the standard pressure attenuation data Y(t) and pressure attenuation data P(t) are worked by the formula: ##EQU5## where P.sub.o, C.sub.o, R.sub.o, and T.sub.o are the standard time upstream gas pressure, constant of gas specific heat ratio, gas constant, and gas temperature, respectively, and P.sub.t, C.sub.t, R.sub.t and T.sub.t are the arrival time upstream gas pressure, constant of gas specific heat ratio, gas constant, and upstream temperature, respectively.